The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
Internal combustion engines combust an air/fuel (A/F) mixture within cylinders to drive pistons and to provide drive torque. Air is delivered to the cylinders via a throttle and an intake manifold. A fuel injection system supplies fuel from a fuel tank to provide fuel to the cylinders based on a desired A/F mixture. To prevent release of fuel vapor, a vehicle may include an evaporative emissions system which includes a canister that absorbs fuel vapor from the fuel tank, a canister vent valve, and a purge valve. The canister vent valve allows air to flow into the canister. The purge valve supplies a combination of air and vaporized fuel from the canister to the intake system.
Closed-loop control systems adjust inputs of a system based on feedback from outputs of the system. By monitoring the amount of oxygen in the exhaust, closed-loop fuel control systems manage fuel delivery to an engine. Based on an output of oxygen sensors, an engine control module adjusts the fuel delivery to match an ideal A/F ratio (14.7 to 1). By monitoring engine speed variation at idle, closed-loop speed control systems manage engine intake airflows and spark advance.
Typically, the fuel tank stores liquid fuel such as gasoline, diesel, methanol, or other fuels. The liquid fuel may evaporate into fuel vapor which increases pressure within the fuel tank. Evaporation of fuel is caused by energy transferred to the fuel tank via radiation, convection, and/or conduction. An evaporative emissions control (EVAP) system is designed to store and dispose of fuel vapor to prevent release. More specifically, the EVAP system returns the fuel vapor from the fuel tank to an engine for combustion therein. The EVAP system is a sealed system to meet zero emission requirements. More specifically, the EVAP system may be implemented in a plug-in hybrid vehicle with minimum engine operation that stores fuel vapor prior to being purged to the engine.
The EVAP system includes an evaporative emissions canister (EEC), a purge valve, and a diurnal control valve. When the fuel vapor increases within the fuel tank, the fuel vapor flows into the EEC. The purge valve controls the flow of the fuel vapor from the EEC to the intake manifold. The purge valve may be modulated between open and closed positions to adjust the flow of fuel vapor to the intake manifold.
Determining whether a fuel leak occurs is important in a closed system. However, adding additional pressure sensors increases the cost of the system.